1. Field of the Invention
The present invention generally relates to antennas. More particularly, the invention relates to Yagi-Uda directional parasitic array antennas at microwave frequencies and low-cost methods for manufacturing the same.
2. Description of the Related Art
xe2x80x9cYagi-Udaxe2x80x9d antennas have been successfully used for many years in applications ranging from the reception of television signals, point-to-point communications and certain types of military electronics. The basic Yagi antenna typically comprises a single driven element, usually a half-wave dipole, which is driven from a source of, or which drives a sink of, electromagnetic energy. Certain non-driven or parasitic elements are arrayed with the dipole. These parasitic elements typically include a reflector element on one side of the dipole and one or more director elements on the other side of the dipole. Each of these several elements are usually positioned in spaced relationship along an antenna axis with the director elements extending in what is referred to as the transmission direction from the dipole. The transmission direction is that direction to which electromagnetic energy is to be received. The length of the elements and the distances between them determine the radiating power of the antenna system.
The prior art to the present disclosure is comprised of several different designs of Yagi-type antennas and methods of fabricating the same. In particular, Skladany U.S. Pat. No. 5,913,549 teaches the disposition of a parasitic element array onto a dielectric substrate. Despite the use of low-cost stamping or photo-etching techniques to produce the directors, the Skladany design uses a separate microwave substrate for the placement of the signal phasing lines, feed lines and driven elements. Unfortunately, the use of a separate microwave substrate increases the cost and weight of the antenna. Moreover, the Skladany method is comprised of numerous steps that increase labor costs in the manufacture of the antennas. The Skladany method first requires that the directors be attached to a substrate or circuit board. Then a second circuit board must be attached to the first. Finally, the feed line is connected to the second circuit board. A low-cost method of designing a single-piece, Yagi-type antenna would clearly be beneficial to the art.
Huang U.S. Pat. No. 5,220,335 discloses a planar microstrip Yagi-type antenna, having a driven element, reflector patches, and one or more director patches, all disposed on a dielectric substrate. Huang teaches that the dielectric constant of the substrate should be between 1.5 and 5. This requires the use of a low-loss, high-cost microwave substrate for the entire length of the antenna array. A substrate of this density will further increase the overall weight of the antenna by a substantial margin. A method of reducing the cost, weight and complexity of such a Yagi-type antenna is desired.
Kerr U.S. Pat. No. 4,118,706 teaches a microstrip-fed directional antenna that uses a rigid aluminum boom for support of the parasitic elements. The boom is then attached to a circuit board that contains the microstrip patch antenna and feed. The thickness of the aluminum boom precludes the use of low-cost manufacturing techniques, such as stamping. The use of a microstrip patch requires a low-loss, high-cost microwave substrate and additional labor to assemble the antenna array. Furthermore, because the microstrip patch circuit board lies in a plane perpendicular to the director array, the diameter of the antenna is increased, thereby precluding the use of small diameter radomes.
Therefore, there is a need for an improved design for a multi-element directional antenna that is manufactured using a simple and low-cost method, such as single or progressive die stamping.
The present invention consists of a novel, multi-element directional antenna and method of making the same. The antenna is a Yagi-type antenna that is formed in one piece from a sheet of conductive material using single and progressive die stamping techniques. The stamped antenna design forms a boom and an array of parasitic elements and a single driven element that radiate therefrom.
The driven element of the stamped antenna design is formed into a folded dipole, using basic folding techniques. This step can either be performed as a part of the initial stamping of the antenna or in a second process. A coaxial feed line is then attached across the gap that is formed by the open ends of the folded dipole driven element.
In a further embodiment of the present invention, the boom may be formed to extend both ends of the array, providing means of supporting the entire antenna within a protective radome.
Thus, a primary objective of the invention is to provide an improved multi-element directional antenna that can be formed in a simple, low-cost manner.
Another objective of the invention is to provide an improved multi-element Yagi-type directional antenna that is formed from a single metal sheet, using low-cost single or progressive die stamping techniques.
Another objective of the invention is to provide an improved, low-cost method of forming Yagi-Uda directional parasitic array antennas at microwave frequencies.
Another objective of the invention is to provide an improved, low-cost method of forming one-piece Yagi-Uda directional parasitic array antennas from a sheet of conductive material, wherein the dipole is formed in unitary construction with the antenna boom using basic element folding techniques.
These and other objectives will be apparent to those skilled in the art.